Ozone chemistry, modeling

Compute the enthalpy change for the destruction of ozone by atomic chlorine by subtracting the dissociation energies of O2 and CIO from the dissociation energy for ozone. What model chemistry is required for accurate modeling of each phase of this process The experimental values are given below (in kcal-moT ) ... 

For those more inclined to use environmental topics to enrich thermodynamics and kinetics parts of the physical chemistry curriculum, Modeling Stratospheric Ozone Chemistry and the Contrail projects are two examples. 

The model tropopause is defined by a PV level of 3.5 pvu poleward of 20° latitude, and by a -2 K km 1 temperature lapse rate equatorward of 20° latitude. Consequently, in this study the troposphere is defined as the volume between the surface and the simulated tropopause. Because the model does not consider typical stratospheric chemical reactions explicitly, ozone concentrations are prescribed from 1-2 levels above the model tropopause up to the top of the model domain at 10 hPa. In both hemispheres we apply monthly and zonally averaged distributions from a 2D stratospheric chemistry model [31]. In the present version of the model, we use the simulated PV and the regression analysis of the MOZAIC data (Section 2) to prescribe ozone in the NH extratropical lower stratosphere, which improves the representation of ozone distributions influenced by synoptic scale disturbances [32, 33]. Furthermore, the present model contains updated reaction rates and photodissociation data [34]. 

Several estimates of the radiative forcing due to changes in tropospheric ozone are based on 3D CTMs. The MOGUNT1A model was used by van Dorland et ah (1997), Berntsen et ah (1997) based their work on the Oslo 3D CTM 1 model, and Roelofs et ah (1997) used ozone changes predicted using the European Centre Hamburg Model version 4 coupled to a tropospheric chemistry model. Forster et ah (1996), on the other hand, used two different 2D CTM models to calculate the ozone increase since pre-industrial time, namely the Cambridge and the UK.MO models. One study was based on observations of ozone. Portmann et ah (1997) estimated tropical tropospheric ozone from ozonesonde profiles and ozone columns derived from satellite maps. 

Yang X, Cox RA, Warwick NJ, Pyle JA, Carver GD, O Connor FM, Savage NH (2005) Tropospheric Bromine Chemistry and Its Impact on Ozone A Model Study. J Geophys Res 110 D23311... 

In recent years, it has become possible to extrapolate accurately using detailed chemical kinetic models to predict quantitatively the behavior of some rather complicated chemical systems. The most famous examples of this success are the detailed atmospheric chemistry models whose predictions underlie the Montreal Protocol on ozone-depleting chemicals. However, these atmospheric chemistry models were developed through a huge international effort over several decades, based heavily on a large number of laboratory experiments. Much more rapid and efficient methods of model development are required for detailed predictive chemical kinetics to become a practical everyday design tool for chemical engineering. 

Prior to the discovery of heterogeneous chemistry, models suggested a strong anti-correlation between estimates of the calculated future midlatitude ozone changes to be expected at steady state due to CFC emissions and that predicted for NOx emissions from supersonic aircraft, as illustrated in Figure 6.8. For a period of more than a decade (roughly 1974 to the mid-1980s), when the estimated future NOx impact on ozone increased, the calculated CFC-related ozone depletion decreased. Of particular importance is the reaction ... 

Fig. 5.19 Modeled ozone flux (in 10 mol s ) into the aqueous phase of a monodis-perse stratiform cloud (droplet radius 5 pm, LWC 0.3 10 ), 30 ppb O3 for different gaseous SO2 concentrations, using a complex cloud chemistry model (Moller and Mauersberger...

Lelieveld, J and R. van Dorland (1995) Ozone chemistry changes in the troposphere and consequent radiative forcing of climate. In Atmospheric ozone as a climate gas General circulation model simulation (Eds. W. S. Wank and I. S. A. Isaksen), NATO ASI Series Vol. 32, Springer, New York, pp. 227-258... 

Atmospheric sciences includes the fields of physics and chemistry and the study of the composition and dynamics of the layers of air that constitute the atmosphere. Related topics include climatic processes, circulation patterns, chemical and particulate deposition, greenhouse gases, oceanic temperatures, interaction between the atmosphere and the ocean, the ozone layer, precipitation patterns and amounts, climate change, air pollution, aerosol composition, atmospheric chemistry, modeling of pollutants both indoors and outdoors, and anthropogenic alteration of land surfaces that in turn affect conditions within the ever-changing atmosphere. 

Bauer, S.E., BaUcanski, Y., Schulz, M., Hauglustaine, D.A., Dentener, F. Global modeling of heterogeneous chemistry on mineral aerosol surfaces influence on tropospheric ozone chemistry and comparison to observations. J. Geophys. Res. 109(EX)2304), 17 (2004). doi 10.1029/ 2003JD003 868... 

Smoydzin, L., von Glasow, R. Modelling chemistry over the Dead Sea bromine and ozone chemistry. Atmos. Chem. Phys. 9, 5057-5072 (2009)... 

In view of this, it has been proposed that hydrated electrons generated on the surface of stratospheric ice crystals, via cosmic rays, could contribute to Cl formation via DEA of adsorbed CFCs. " Photodetachment of the chloride ions might then provide a mechanism to generate the Cl radicals that lead to ozone destruction. However, attempts to link these laboratory observations directly to stratospheric ozone chemistry have been strongly criticized, " although modeling does leave open the possibility that, at the very least, HCl destruction on ice crystals might be important for stratospheric chlorine chemistry. More work is evidently needed to resolve this controversy. 

By combining models of meteorology and ozone, Paul pioneered the field of atmospheric chemistry, and showed how local emissions can have a global effect, even though the substances in question occur in minute, i.e., trace amounts. With his work, that has had an impact well beyond his own field, he followed in the footsteps of pioneers in chemistry in the past centuries such as Scheele, Priestley, Lavoisier, and Laplace. Like Paul, they were also intrigued by the chemical composition of air, what controls it, and tried to unravel its importance for life on Earth. The central role of nitrogen oxides in stratospheric ozone chemistry was the first of Paul s impressive series of discoveries. 

Heterogeneous chemistry occurring on polar stratospheric cloud particles of ice and nitric acid trihydrate has been estabUshed as a dorninant factor in the aggravated seasonal depletion of o2one observed to occur over Antarctica. Preliminary attempts have been made to parameterize this chemistry and incorporate it in models to study ozone depletion over the poles (91) as well as the potential role of sulfate particles throughout the stratosphere (92). 

Because of the expanded scale and need to describe additional physical and chemical processes, the development of acid deposition and regional oxidant models has lagged behind that of urban-scale photochemical models. An additional step up in scale and complexity, the development of analytical models of pollutant dynamics in the stratosphere is also behind that of ground-level oxidant models, in part because of the central role of heterogeneous chemistry in the stratospheric ozone depletion problem. In general, atmospheric Hquid-phase chemistry and especially heterogeneous chemistry are less well understood than gas-phase reactions such as those that dorninate the formation of ozone in urban areas. Development of three-dimensional models that treat both the dynamics and chemistry of the stratosphere in detail is an ongoing research problem. 

The horizontal dispersion of a plume has been modeled by the use of expanding cells well mixed vertically, with the chemistry calculated for each cell (31). The resulting simulation of transformation of NO to NO2 in a power plant plume by infusion of atmospheric ozone is a peaked distribution of NO2 that resembles a plume of the primary pollutants, SO2 and NO. The ozone distribution shows depletion across the plume, with maximum depletion in the center at 20 min travel time from the source, but relatively uniform ozone concentrations back to initial levels at travel distances 1 h from the source. 

Approaches used to model ozone formation include box, gradient transfer, and trajectoty methods. Another method, the particle-in-cell method, advects centers of mass (that have a specific mass assigned) with an effective velocity that includes both transport and dispersion over each time step. Chemistry is calculated using the total mass within each grid cell at the end of each time step. This method has the advantage of avoiding both the numerical diffusion of some gradient transfer methods and the distortion due to wind shear of some trajectory methods. 

You ll need to run five calculations at each model chemistry oxygen atom, chlorine atom, O2, CIO and ozone (but don t forget that you can obtain lower-level energies from a higher-level calculation). Use the experimental geometries for the various molecules and the following scaled zero-point energy corrections ... 

The chemistry of the stratospheric ozone will be sketched with a very broad brush in order to illustrate some of the characteristics of catalytic reactions. A model for the formation of ozone in the atmosphere was proposed by Chapman and may be represented by the following "oxygen only" mechanism (other aspects of... 

This brief description of oxidant formation in polluted air is based on our current understanding of the chemistry involved. It is evident fix>m an examination of the detailed mechanism that many of the important reactions have not been well studied. For example, the sequences of degradation reactions for the hydrocarbons are only poorly understood. As a result of these uncertainties, it is not possible to make accurate predictions of photochemical oxidant concentrations. However, with another 5 yr of progress similar to the last 5, it should be possible to construct chemical models that will permit ozone predictions accurate to within... 

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